1. Field of the Invention
The present invention relates to the structure and process of forming of piezoelectric transducer, and an actuator using the piezoelectric transducer.
2. Description of Related Art
Actuators utilizing piezoelectric transducers are highly efficient in converting electrical energy to motive energy, and generating large amounts of motive energy though being compact and lightweight. In addition, the motive energy generated by the piezoelectric transducer can be easily regulated. All of these characteristics make actuators utilizing piezoelectric transducers ideal for use in positioning and moving driven members in cameras, test instruments and other precision equipment.
The piezoelectric transducer which serves as the drive source used in this kind of actuator is comprised of a plurality of piezoelectric elements laminated together. This configuration allows the largest possible physical displacement in the direction of piezoelectric element thickness to be obtained in response to an applied voltage.
FIG. 22(a) is an oblique view showing the external structure of the piezoelectric transducer comprised of a plurality of piezoelectric elements laminated together. A piezoelectric transducer 100 is comprised of a plurality of individual piezoelectric elements 101 each being about 100 micrometers thick and provided on one surface with an electrode 102. Every other electrode 102 (between facing piezoelectric elements) is connected to a line 103 as the positive terminal while the remaining electrodes 102 are connected to the line 104 as the negative terminal as shown in FIG. 22(b). Since the thickness of the piezoelectric transducer changes as a voltage is applied between the positive and negative terminals, the changes in the thickness or displacement can be transmitted through an appropriate means to drive or position the driven member.
FIG. 23 is a cross-sectional view showing the actuator using the piezoelectric transducer comprised of a plurality of piezoelectric element units as described above. FIG. 24 is a cross sectional view showing the friction coupling of the actuator.
In FIG. 23, the reference numeral 111 denotes a frame, 112, 113, 114 are support blocks and 115 is a drive shaft. The drive shaft 115 is supported by the support block 113 and the support block 114 to allow axial movement. One end of the piezoelectric transducer 100 is affixed to the support block 112 and affixed at the other end to the drive shaft 115. The drive shaft 115 is supported to allow axial displacement (direction of arrow a and its opposite direction) in response to displacement in the direction of thickness of the piezoelectric transducer 100.
The drive shaft 115 passes through a slider block 116. An aperture 116a is formed, as shown in FIG. 24, in the lower part of the slider block 116 through which the drive shaft 115 passes and the lower half of the drive shaft 115 is thus exposed. In this aperture 116a, a pad 117 is fitted to engage with the lower half of the drive shaft 115, and a protrusion 117a is formed in the lower section in the pad 117 (See FIG. 24). The protrusion 117a of the pad 117 is pressed upwards by a plate spring 118 and an upward force F is thus applied on the pad 117 to contact the drive shaft 115.
A table 120 for placement of objects is secured to the slider block 116 with machine screws 121.
In the above arrangement, the drive shaft 115 and slider block containing the pad 117 are press-contacted by the force F of the plate spring 118 and friction coupled.
The operation is described next. First of all, when a sawtooth waveform pulse having a gentle rising part and a steep falling part is applied to the piezoelectric transducer 100, the gentle rising part of the drive pulse causes the piezoelectric transducer 100 to elongate, displacing in the direction of thickness, and the drive shaft 115 coupled to the piezoelectric transducer 100 also displaces slowly in the direction of the arrow "a". The slider block 116 at this time friction coupled to the drive shaft 115 moves in the direction of the arrow "a" along with the drive shaft 15 due to the friction coupling force.
The steep falling part of the drive pulse causes the piezoelectric transducer 100 to contract, displacing in the direction of thickness, and the drive shaft 115 coupled to the piezoelectric transducer 100 also displaces swiftly in the opposite direction of the arrow "a". The slider block 116 at this time friction coupled to the drive shaft 115 is effectively stopped in the current position and does not move, due to the cancelling out of the friction coupling force by the inertia of the slider block 116. The slider block 116 and the table attached to the slider block 116 can be moved consecutively in the direction of the arrow "a" by means of consecutive application of drive pulses to the piezoelectric transducer 100.
In order to move the slider block 116 and the table 120 in the opposite of the previous direction (opposite direction of arrow "a"), the sawtooth drive pulse waveform applied to the piezoelectric transducer 100 is changed and a drive pulse consisting of a steep rising part and a gentle falling part can then be applied to achieve movement in the opposite direction.
The above description also effectively takes into account that a sliding motion is added to the friction coupled surfaces between the slider block 116 and the drive shaft 115 whether moving in the direction of the arrow "a" or the opposite direction and objects moving in direction of the arrow "a" are also included due to the difference in drive times.
Among other configurations of the piezoelectric transducer is a piezoelectric transducer formed in hollow tubular shape of a single layer. FIG. 25 is a cross sectional view showing one configuration of the hollow tubular shaped single layer piezoelectric transducer 134. In FIG. 25, an electrode 136 and an electrode 137 are formed on the outer surface of the single layer, hollow tubular piezoelectric transducer 134, and an electrode 138 is formed on the inner surface of the hollow cylinder.
The single layer, hollow tubular piezoelectric transducer 134 is supported by support members 132, 133 installed on the right and left of a mount 131. A slider 135 is friction coupled to the hollow tubular piezoelectric transducer 134 by an appropriate amount of frictional force. A plug 133a is installed to fit in with one end of the piezoelectric transducer 134 and this plug 133a screws into the support member 133 so that the piezoelectric transducer 134 is secured and supported by the mount 131.
In this configuration, a first electrode section comprised of an electrode 136 and an electrode 138; and a second electrode section comprised of an electrode 137 and an electrode 138, are both polarized beforehand in the same radial direction. When sawtooth wave pulses of mutually reverse polarities are applied to the first electrode section and the second electrode section while in this state, an elongation displacement occurs at the first electrode section and a contraction displacement occurs at the second electrode section during the gentle rising part of the sawtooth waveform pulse, and the slider 135 can move in the direction of the arrow "a". Further, on the steep falling part of the sawtooth waveform pulse a sudden contraction displacement occurs at the first electrode section and a sudden elongation displacement occurs at the second electrode section however the inertia of the slider 135 cancels out the force of the frictional coupling with the piezoelectric transducer 134 and there is no sliding movement on their surfaces. Thus by transmitting the movement of the slider 135 to the drive section of a transducer by a suitable means, the positioning and driving of a drive member can be achieved.
The piezoelectric transducer of the conventional art configured as related above with a plurality of laminations of piezoelectric elements was fabricated by means of a complex process consisting of a process to install electrodes in the respective surfaces of the individual piezoelectric elements, a process to bond or adhere the laminations, and a process to wire the electrodes of each layer. These complex processes had the drawback of a high manufacturing cost.
Further, even though the hollow tubular shaped single layer piezoelectric transducer had the characteristic of comparatively high mechanical strength, increasing the intensity of the electrical field was required in order to increase the displacement generated by the piezoelectric element. Accordingly, when there are limitations on the voltage that can be applied to the piezoelectric element, the thickness of the piezoelectric transducer had to be reduced to raise the intensity of the electrical field. In other words, the problem arose that when increasing the displacement generated by the piezoelectric transducer was attempted, the mechanical strength of the piezoelectric transducer declined.